The present invention relates generally to fuel injectors, and more particularly, to fuel injectors useful for gas turbine combustion engines.
Fuel injectors useful for such applications as gas turbine combustion engines, direct pressurized fuel from a manifold to one or more combustion chambers. Fuel injectors also function to prepare the fuel for mixing with air prior to combustion. Each injector typically has an inlet fitting connected to the manifold, a tubular extension or stem connected at one end to the fitting, and one or more spray nozzles connected to the other end of the stem for directing the fuel into the combustion chamber. A fuel passage (e.g., a tube or cylindrical passage) extends through the stem to supply the fuel from the inlet fitting to the nozpzle. Appropriate valves and/or flow dividers can be provided to direct and control the flow of fuel through the nozzle. The fuel injectors are often placed in an evenly-spaced annular arrangement to dispense (spray) fuel in a uniform manner into the combustor chamber. Additional concentric and/or series combustion chambers each require their own arrangements of nozzles that can be supported separately or on common stems. The fuel provided by the injectors is mixed with air and ignited, so that the expanding gases of combustion can, for example, move rapidly across and rotate turbine blades in a gas turbine engine to power an aircraft, or in other appropriate manners in other combustion applications.
A fuel injector typically includes one or more heat shields surrounding the portion of the stem and nozzle exposed to the heat of the combustion chamber. The heat shields are considered necessary because of the high temperature within the combustion chamber during operation and after shut-down, and prevent the fuel from breaking down into solid deposits (i.e., xe2x80x9ccokingxe2x80x9d) which occurs when the wetted walls in a fuel passage exceed a maximum temperature (approximately 400xc2x0 F. (200xc2x0 C.) for typical jet fuel). The coke in the fuel nozzle can build up and restrict fuel flow through the fuel nozzle rendering the nozzle inefficient or unusable.
One particularly useful heat shield assembly is shown in Stotts, U.S. Pat. No. 5,598,696, owned by the assignee of the present application. This heat shield assembly includes a pair of U-shaped heat shield members secured together to form an enclosure for the stem portion of the fuel injector. At least one flexible clip member secures the heat shield members to the injector at about the midpoint of the injector stem. The upper end of the heat shield is sized to tightly receive an enlarged neck of the injector to prevent combustion gas from flowing between the heat shield members and the stem. The clip member thermally isolates the heat shield members from the injector stem. The flexibility of the clip member permits thermal expansion between the heat shield members and the stem during thermal cycling, while minimizing the mechanical stresses at the attachment points.
Another useful stem and heat shield assembly is shown in Pelletier, U.S. patent application Ser. No. 09/031,871, filed Feb. 27, 1998, and also owned by the assignee of the present application. In this heat shield assembly, the fuel tube is completely enclosed in the injector stem such that a stagnant air (dry territory) gap is provided around the tube. The fuel tube is fixedly attached at its inlet end and its outlet end to the inlet fitting and nozzle, respectively, and includes a coiled or convoluted portion which absorbs the mechanical stresses generated by differences in thermal expansion of the internal nozzle component parts and the external nozzle component parts during combustion and shut-down.
Many fuel tubes also require secondary seals (such as elastomeric seals) and/or sliding surfaces to properly seal the heat shield to the fuel tube during the extreme operating conditions occurring during thermal cycling.
While such heat shield assemblies as described above are useful in certain applications, they require a number of components, and additional manufacturing and assembly steps, which can increase the overall cost of the injector, both in terms of original purchase as well as a continuing maintenance. In addition, the heat shield assemblies can take up valuable space in and around the combustion chamber, block air flow to the combustor, and add weight to the engine. This can all be undesirable with current industry demands requiring reduced cost, smaller injector size (xe2x80x9cenvelopexe2x80x9d) and reduced weight for more efficient operation.
Because of limited fuel pressure availability and a wide range of required fuel flow, many fuel injectors include pilot and secondary nozzles, with only the pilot nozzles being used during start-up, and both nozzles being used during higher power operation. The flow to the secondary nozzles is reduced or stopped during start-up and lower power operation. Such injectors can be more efficient and cleaner burning than single nozzle fuel injectors, as the fuel flow can be more accurately controlled and the fuel spray more accurately directed for the particular combustor requirement. The pilot and secondary nozzles can be contained within the same nozzle stem assembly or can be supported in separate nozzle assemblies. Dual nozzle fuel injectors can also be constructed to allow further control of the fuel for dual combustors, providing even greater fuel efficiency and reduction of harmful emissions.
As should be appreciated, fuel injectors with pilot and secondary nozzles require complex and sophisticated routing of the fuel to the spray orifices in the nozzle. The fuel not only has to be routed through the nozzle portion of the fuel injector, but also through the stem. Such routing becomes all the more complex in multiple nozzle arrangements, where multiple nozzles are fed along a common stem. The routing also becomes more complex if cooling circuits are included to cool the nozzle portion of the injector.
A typical technique for routing fuel through the stem portion of the fuel injector is to provide concentric passages within the stem, with the fuel being routed separately through different passages. The fuel is then directed through passages and/or annular channels in the nozzle portion of the injector to the spray orifice(s). Mains, U.S. Pat. No. 5,413,178, for example, which is also owned by the assignee of the present application, shows concentric passages where the pilot fuel stream is routed down and back along the secondary nozzle for cooling purposes. This can also require a number of components, and additional manufacturing and assembly steps, which can all be contrary to the demands of cost reduction and weight, and small injector envelope.
With current trends toward developing even more efficient and cleaner-burning combustors, it is a continuing challenge to develop improved fuel injectors to properly deliver fuel to a combustion chamber for operation of the gas turbine engine, and which will fit into a small envelope, have a reduced weight, fewer components, and can be manufactured and assembled in an economical manner.
The present invention provides a novel and unique fuel injector for directing fuel from a manifold and dispensing the fuel within the combustion chamber of a combustion engine. The fuel injector can include multiple fuel circuits, single or multiple nozzle assemblies, and cooling circuits. The injector overall has few components for weight reduction and thereby increased fuel efficiency. The fuel injector of the present invention also fits within a small envelope and is economical to manufacture and assemble. In many applications, the fuel injector reduces the need for heat shielding around the stem of the injector, for additional reliability, weight and cost reduction. The fuel injector is particularly useful for gas turbine combustion engines on airplanes, but can also be useful in other combustion applications.
According to the present invention, the fuel injector includes an inlet fitting, a stem connected at one end to the inlet fitting, and one or more nozzle assemblies, connected to the other end of the stem and supported at or within the combustion chamber of the engine. An elongated feed strip extends through the stem to the nozzle assemblies to supply fuel from the inlet fitting to the nozzle(s) in the nozzle assemblies. The upstream end of the feed strip can be directly attached (such as by brazing or welding) to the inlet fitting without additional sealing components (such as elastomeric seals). The downstream end of the feed strip is preferably connected in a unitary (one-piece) manner to the nozzle. The feed strip has convolutions along its length to provide increased relative displacement flexibility along the axis of the stem and reduce stresses caused by differential thermal expansion due to the extreme temperatures in the combustion chamber. The need for additional heat shielding of the stem portion of the injector can therefore be reduced, if not eliminated in many applications.
The feed strip and nozzle are preferably formed from a plurality of plates. Each plate includes an elongated, feed strip portion and a unitary head (nozzle) portion, substantially perpendicular to the feed strip portion. Passages and openings in the plates are formed by selectively etching the surfaces of the plates. The plates are then arranged in surface-to-surface contact with each other and fixed together such as by brazing or diffusion bonding, to form an integral structure. Selectively etching the plates allows multiple fuel circuits, single or multiple nozzle assemblies and cooling circuits to be easily provided in the injector. The etching process also allows multiple fuel paths and cooling circuits to be created in a relatively small cross-section, thereby reducing the size of the injector.
The feed strip portion of the plate assembly is then mechanically formed (bent) to provide the convoluted form. In one form of the invention the plates all have a T-shape in plan view. In this form, the head portions of the plate assembly can be mechanically formed (bent) into a cylinder, or other appropriate shape. The ends of the head can be spaced apart from one another, or can be brought together and joined, such as by brazing or welding. Spray orifices are provided on the radially outer surface, radially inner surface and/or ends of the cylindrical nozzle to direct fuel radially outward, radially inward and/or axially from the nozzle. The integral feed strip and nozzle unit requires only a small envelope, is economical to manufacture and assemble, and it is believed will have reduced maintenance and service costs over time.
Thus, as described above, a novel and unique fuel injector for combustion engines is provided which directs fuel from a manifold to a combustion chamber. The fuel injector is economical to manufacture and assemble, and can be incorporated into a small envelope. The injector has few components for weight reduction, which thereby increases the fuel efficiency of the engine.
Further features and advantages of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings.